Stepping motor controllers of the general type being described are discussed in the following U.S. Pat. Nos. 4,297,625; 4,121,145; 4,151,449; 4,119,902; 4,145,644, 4,100,471; 4,091,316; 4,125,801; 4,284,940; 4,306,181; 3,906,319; 3,885,210; and 4,087,732.
A drawback of prior micro-stepping controllers is that the stepped periodic functions for controlling the motor could not be selected, say, sinusoidal and/or were not designed for rapid change in resolution (the number of micro-steps per revolution).
Another drawback of prior micro-stepping controllers is the number of components required.